Questions & Answers

Light from the Sun reaches the earth approximately in
(A) $ 5s $
(B) $ 50s $
(C) $ 500s $
(D) $ 0.5s $

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Hint: The light from the sun travels a distance and reaches earth. We know that light travels with a given constant velocity. If we know the distance between the sun and the earth, we can calculate the time taken by the light to reach the earth using the distance and velocity of light.

Formula used:
 $ v = \dfrac{x}{t} $
where $ v $ stands for the velocity of the moving object, $ x $ stands for the distance travelled by the object and $ t $ stands for the time taken by the object to cover the distance.

Complete step by step solution
We know the velocity with which light travels and the distance between the sun and the earth. Using these values we can easily calculate the time taken for the light from the sun to reach earth.
The distance between the earth and the sun is nearly $ 150 $ million kilometres.
We know that, the velocity of light,
 $ c = 3 \times {10^8}m/s = 300000km/s $
We know that the formula for velocity is,
 $ v = \dfrac{x}{t} $
Here $ v = c $ and we can write the formula for time from the above formula as,
 $ t = \dfrac{x}{v} $
We know that, $ x = 150000000km $
and $ v = 300000km/s $
Substituting the values in the above equation, we get
 $ t = \dfrac{{150000000km}}{{300000km/s}} = 500s $
Therefore, the answer is: Option (C); $ 500s $ .

Additional information
Sun’s energy reaches the earth by means of radiation, conduction and convection. Photons from the surface of the sun travel through the vacuum and reach the surface of the earth.

To answer this question we need to know the distance between the sun and the earth and the velocity of light through vacuum. The time taken by the light to reach different planets in the solar system varies with their distance from the sun. It takes only $ 3 $ minutes for the sunlight to reach mercury and it will take $ 5.3 $ hours for the sunlight to reach pluto.